With the development of display technology, the Thin Film Transistor Liquid Crystal Display (TFT-LCD), such as Liquid Crystal Display (LCD) possesses advantages of high image quality, power saving, thin body and wide application scope. Thus, it has been widely applied in various consumer electrical products, such as mobile phone, television, personal digital assistant, digital camera, notebook, laptop, and becomes the major display device.
Most of the liquid crystal displays on the present market are back light type liquid crystal displays, which comprise a liquid crystal display panel and a back light module. The working principle of the liquid crystal display panel is to locate liquid crystal molecules between two parallel glass substrates, and a plurality of vertical and horizontal tiny electrical wires are between the two glass substrates. The light of back light module is reflected to generate images by applying driving voltages to control whether the liquid crystal molecules to be changed directions. Generally, the liquid crystal display panel comprises a CF (Color Filter) substrate, an array substrate, LC (Liquid Crystal) sandwiched between the CF substrate and TFT substrate and sealant. The formation process generally comprises: a forepart Array process (thin film, photo, etching and stripping), a middle Cell process (Lamination of the array substrate and the CF substrate) and a post module assembly process (Attachment of the driving IC and the printed circuit board). The forepart Array process is mainly to form the array substrate for controlling the movement of the liquid crystal molecules; the middle Cell process is mainly to add liquid crystal between the array substrate and the CF substrate; the post module assembly process is mainly the driving IC attachment and the integration of the printed circuit board. Thus, the liquid crystal molecules are driven to rotate and display pictures. The TFT-LCD array substrate comprises a plurality of scan lines, a plurality of data lines and a plurality of common electrode lines. The plurality of scan lines and the plurality of data lines define a plurality of pixel units. Each pixel unit comprises a thin film transistor and a pixel electrode. The gate of the thin film transistor is coupled to the corresponding gate line. As the voltage of the gate line reaches the activation voltage, the source and the drain are conducted, and the data voltage of the data line is inputted to the pixel electrode.
For the TFT-LCD in the mainstream market, three types, which can be categorized according to the driving modes of the liquid crystal, respectively are Twisted Nematic (TN), Super Twisted Nematic (STN), In-Plane Switching (IPS) and Vertical Alignment (VA). The IPS mode utilizes the electric field which is roughly parallel with the substrate surface to drive the liquid crystal molecules twisting along the substrate surface for response, and thus possesses excellent view angle property. Therefore, it is applied in kinds of TV display applications.
The structure of the IPS TFT-LCD array substrate is shown in FIG. 1. Each pixel unit comprises a gate 101 located on the substrate 100, a gate isolation layer 102 located on the gate 101 and the substrate 100, a semiconductor layer 103 located on the gate isolation layer 102, a source 104, a drain 105 located on the semiconductor layer 103 and the gate isolation layer 102, an insulation protective layer 106 located on the source 104, the drain 105, the semiconductor layer 103 and the gate isolation layer 102, and a pixel electrode 107 located on the insulation protective layer 106; moreover, in the array substrate, the common electrode layer 120, the gate 101 and the gate scan lines 110 are manufactured with the same metal layer, and the pixel electrode 107 is coupled to the drain 105 through the via structure in the insulation protective layer 106, because the resistance between the pixel electrode 107 and the drain 105 will influence the charge efficiency of the pixel electrode 107, the pixel electrode 107 cannot be charged to the ideal voltage in the scan duration of this row if the resistance is over large, and the display effect is affected. The factors of influencing the via contact resistance are many, such as the interface electron barrier height, the via size and the via overlap.